We have a vs commodore sedan. There is enough room for 3 carseats across the back and pram and groceries in the boot. I think if there is ANY chance you are going to go for number 4 you would be better going for a 7 seater. We have had to upgrade 2 times due to having more kids, the 1st one was a little 2 door and couldn't fit a reverse carseat in, and the 2nd one couldn't fit 3 carseats across the back.
Ditto that. We went from a Ford Focus to a Ford Falcon to a Toyota Kluger to a Toyota Tarago. If your going to stick with just the 3, I can recommend the Kluger if your looking for an SUV. Or Falcon is a bit squishy for 3 carseats and a pram + other things in the boot. Ive heard the wagon's are great though.